ever heard someone who isn't good in mandarin try to be smart and use mandarin idioms and sayings? the outcome was rather amusing wasn't it?

because the person used an inappropriate phrase, or words taken out of context, meanings are changed, laughter ensued, and the person is left feeling, and looking, rather stupid.

ignorance. that person was ignorant to the true meanings of the words that he/she used, thus hitting himself/herself on the mouth, or scoring an own goal, so to speak.